Terahertz absorption by excitonic polaritons

TL;DR

This paper analyzes terahertz absorption spectra of excitonic polaritons in quantum dots, revealing how spectral features indicate the system's thermalization state, with implications for understanding light-matter interactions in strongly coupled systems.

Contribution

It provides a theoretical framework for interpreting terahertz absorption spectra of excitonic polaritons, linking spectral features to thermalization and non-equilibrium states.

Findings

Spectral peaks correspond to exciton transitions and are affected by polariton effects.

Thermalized systems show a peak at the 1s - 2p exciton transition.

Non-equilibrium systems exhibit absorption peaks at low energies.

Abstract

We use linear response theory in order to compute the light absorption spectrum, in the terahertz band, of a polariton system composed by excitons in a quantum dot very strongly coupled to the lowest photon mode of a thin micropillar. In a thermalized (Bose condensed) system at low temperatures, the spectral function shows a peak (GDR) associated to a 1s - 2p exciton transition, enhanced by polariton effects. On the other hand, in a non-equilibrium system absorption is peaked at low energies. Thus, a measurement of terahertz absorption could give an indication of the degree of thermalization in the polariton system.